Sewing machine having a thread finger assembly

ABSTRACT

A thread finger assembly for a sewing machine has at least one thread finger. The latter can be actuated between a loop engagement position and a loop pull-out position. The loop engagement position serves for the engagement of the thread finger in a thread loop generated by the sewing machine in a stitch forming region. The loop pull-out position is displaced relative to the loop engagement position for pulling out the thread loop with the thread finger, away from the stitch forming area. A thread finger drive serves for actuating the thread finger between the loop engagement position and the loop pull-out position. This results in an assembly of a sewing machine with which an appealing seam pattern is generated in a reproducible manner at a seam beginning.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a national phase entry of international patent application PCT/EP 2020/057 855, filed Mar. 20, 2020, and claims the priority of German patent application DE 10 2019 205 303.3, filed Apr. 12, 2019, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a sewing machine having a thread finger assembly.

BACKGROUND

Sewing machines are known in many embodiments, for example from EP 3 088 589 B1, EP 3 360 994 A1, U.S. Pat. No. 6,276,289 B1 and DE 10 2013 107 270 B3.

DE 20 2012 104 187 U1 discloses a chain stitch sewing machine. DE 87 13 500 U1 discloses a double chain stitch sewing machine with a hook and a hook thread spreader.

SUMMARY

It is an object of the present invention to further develop an assembly of a sewing machine such that an appealing seam pattern is generated in a reproducible manner at a seam beginning.

This object is achieved according to the invention by a sewing machine with a thread finger assembly

-   -   with at least one thread finger, which can be actuated between a         -   loop engagement position for the engagement of the thread             finger in a thread loop generated by the sewing machine in a             stitch forming region and a         -   loop pull-out position, which is displaced away from the             stitch forming region relative to the loop engagement             position for pulling out the thread loop with the thread             finger,     -   with a thread finger drive for actuating the thread finger         between the loop engagement position and the loop pull-out         position,     -   wherein in the loop engagement position a fingertip of the at         least one thread finger is located between a hook and a stitch         plate of the sewing machine.

According to the invention, it has been found that with the aid of a thread finger assembly with at least one thread finger, thread beginning portions may be drawn away from a visible region of the sewing material in a controlled manner at the seam beginning. In this case, there is no thread beginning portion in the visible region that might spoil the visual appearance. The sewn seam begins with a neat stitch.

In the loop engagement position, the fingertip of the at least one thread finger is located between a hook and a stitch plate of the sewing machine. Such an arrangement of the fingertip of the at least one thread finger enables secure catching of the thread loop.

The loop pull-out position of the at least one thread finger may at the same time be a neutral position of the thread finger, in which it may remain during further sewing after its use at the seam beginning. The thread loop pulled out by the thread finger of the thread finger assembly may be an upper thread loop.

The thread finger may be of small thickness.

A bent embodiment of the at least one thread finger according to the invention results in the thread finger occupying very little installation space during its displacement movement in the critical stitch forming region.

The bending of the bent thread finger embodiment may be adapted to a displacement movement of the thread finger with respect to its curvature, so that a trajectory of the thread finger is at least approximately bent like the thread finger.

A catcher hook disposed at the free end of the at least one thread finger has proven to be particularly suitable for securely catching the thread loop.

A thread finger assembly having two thread fingers which can be assigned to two thread loops of a two-needle sewing machine may be used together with a two-needle sewing machine.

A slotted guide for guiding a displacement movement of the thread finger between the loop engagement position and the loop pull-out position has proven to be particularly suitable for guiding the displacement movement in a reproducible and quick manner.

This applies correspondingly to the thread finger drive designed as a pneumatic drive. Alternatively, an electric motor drive may be used as the thread finger drive.

The sewing machine may be a chain stitch sewing machine and, in particular, a double chain stitch sewing machine.

A thickness of the thread finger in the direction of the distance between the hook and the stitch plate of the sewing machine which is at most 2 mm makes it possible to guide a hook tip of the hook close to the stitch plate despite the finger tip of the thread finger being intermediate in the loop engagement position, which leads to the possibility of working with short thread loops and correspondingly to short possible thread beginning portions and thread end portions. The distance between the hook and the stitch plate where the thread finger engages between these two components need only be configured slightly larger than the thickness of the thread finger, for example at most 2 mm larger than the thickness of the thread finger. The thickness of the thread finger in the direction of the distance between the hook and the stitch plate is preferably at most 1.8 mm and may in particular be at most 1.5 mm.

A small width of the thread finger transverse to its longitudinal extension being smaller than 5 mm allows a clean engagement even with small thread loops, which in turn keeps the maximum thread length required for the thread loop advantageously small. The width of the thread finger transverse to the longitudinal extension thereof may be less than 4 mm, may be less than 3 mm and may also be less than 2 mm.

An embodiment of the invention is explained in more detail below with reference to the drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 perspectively shows main components of a sewing machine of a sewing system for sewing, in particular, seams located multi-dimensionally in space;

FIG. 2 from a viewing direction similar to FIG. 1, shows a magnified thread finger assembly of the sewing machine, wherein thread fingers of the thread finger assembly are in a loop engagement position for the engagement in thread loops generated by the sewing machine in a stitch forming region;

FIG. 3 perspectively, in a front view, shows stitch forming components of the sewing machines, including the thread fingers, again in the loop engagement position;

FIG. 4 in a view similar to FIG. 3, shows the stitch forming components with the thread fingers of the thread finger assembly in a loop pull-out position which is displaced in an obliquely downward manner away from the stitch forming region relative to the loop engagement position for pulling out the thread loops; and

FIG. 5 shows a side view from viewing direction V in FIG. 1 of the stitch forming components shown in FIGS. 3 and 4, with the thread fingers displaced from the loop engagement position.

DETAILED DESCRIPTION

A sewing system serves for sewing multi-dimensional seams and in particular seams that are not evenly located three-dimensionally in space. An application example for the sewing system is the attachment of decorative seam applications in the interior space of vehicles, for example on instrument panels, door side panels or arm rests. The sewing system includes a sewing machine 1, main components of which are shown in FIG. 1. The sewing machine 1 is supported by an arm of a robot, which is not shown in more detail, with which the sewing machine 1 may be controlled in a random manner to be oriented in space in five or six degrees of freedom.

The sewing machine 1 is a double chain stitch sewing machine.

For facilitating positional relations, a Cartesian xyz coordinate system is indicated in each of the figures. The x-axis, along which the seam is generated in an initial position of stitch forming tools described in more detail below, runs obliquely to the rear left in FIG. 1. The y-axis runs obliquely to the front left in FIG. 1 and the z-axis runs upwards in FIG. 1.

The sewing machine 1 has a housing 2 with a C-shaped basic structure parallel to the yz plane with a housing upper part 3, a housing lower part 4 and a stand 5 connecting these two parts to form the C shape. The housing upper part 3 and the housing lower part 4 run along the y direction. The stand runs along the z-direction.

As stitch forming components, the sewing machine 1 has two sewing needles 6, 7 (cf. FIG. 5) which are carried by a common needle bar 8. The needle bar 8 is mounted in a needle bar upper part driven up and down parallel to the z-axis in the housing upper part 3.

Two hooks 9, 10 (cf. FIG. 5) serve as further stitch forming components, which are mounted on a hook lower part 11 and driven synchronously with the sewing needles 6, 7 for stitch formation. The hooks 9, 10 are designed as swing or pendulum hooks swinging about an axis parallel to the y-axis. The hooks 9, 10 may be designed to form a chain stitch. The hooks 9, 10 may be designed as inline hooks.

The hook lower part 11 forms a column of the sewing machine 1. The hook lower part 11 is mounted to the housing lower part 4. Due to the column design of the hook lower part 11, a stitch forming region in which the seam is generated by the sewing machine 1 is very freely accessible from all sides.

During the stitch formation, the two sewing needles 6, 7 are driven up and down along a longitudinal needle bar axis. Synchronously to this, a swivelling movement of the hooks 9, 10 is driven.

During the stitch formation, the two sewing needles 6, 7 penetrate stitch holes in a stitch plate 11 a on which the sewing material rests during the stitch formation. The stitch plate 11 a is arranged above the hook lower part 11 with the two hooks 9, 10 and is configured to be bent in a manner complementary to the swinging movement of the hooks 9, 10.

These stitch forming movements of the sewing needles 6, 7 and the hooks 9, 10 are driven by a sewing drive motor which is accommodated in the stand 8 of the housing 5.

The sewing machine 1 has a thread finger assembly 12, which is shown as a whole in FIG. 2. The thread finger assembly 12 serves to pull an upper thread 13 (cf. FIG. 4) downwardly from a sewing material visible region after a first stitch of the sewing machine 1, thereby ensuring a neat seam pattern.

The thread finger assembly 12 has two thread fingers 14, 15. Each of these thread fingers 14, 15 is assigned to one of the two stitch forming component pairs sewing needle 6/hook 9 and sewing needle 7/hook 10. At their free ends, the two thread fingers 14, 15 each have a thread catcher hook 15 a. An extension of the thread fingers 14, 15 along the z-direction, that is to say a thickness of the thread fingers, is at most 2 mm A width of the thread fingers 14, 15 along the y-direction is at most 5 mm.

The two thread fingers 14, 15 can be actuated between a loop engagement position shown in FIGS. 1 to 3 and a loop pull-out position displaced downwards relative thereto, which is shown in FIG. 4.

In the loop engagement position, the thread fingers 14, 15 engage a thread loop of the respective upper thread 13 generated by the sewing machine 1 in the stitch forming region. Here, the thread finger 14 engages the upper thread loop guided by the sewing needle 6 and the thread finger 15 engages the upper thread loop guided by the sewing needle 7. This engagement takes place below the sewing material resting on the stitch plate. In the loop engagement position, fingertips of the two thread fingers 14, 15 are located between the respective hook 9, 10 and the stitch plate 11 a.

In the loop pull-out position, the two thread fingers 14, 15 are displaced away from the stitch forming region relative to the loop engagement position for pulling out the upper thread loops, as shown by a comparison of FIGS. 3 and 4.

The two thread fingers 14, 15 are configured as to be bent. A bending of the thread fingers 14, 15 is adapted with respect to its curvature to a curvature of a displacement movement between the loop engagement position and the loop pull-out position. Thus, a trajectory of the thread fingers 14, extends as to be bent approximately like the thread fingers 14, 15 themselves. This trajectory as well as the curvature of the thread fingers 14, 15 is in turn designed as to be complementary to the bent design of the stitch plate 11 a as well as to the swinging movement of the hooks 9, 10, so that the thread finger movement is possible without interference in the small installation space between the stitch plate 11 a and the hooks 9, 10.

This trajectory of the displacement movement of the thread fingers 14, 15 is predetermined by a slotted guide 16. The latter comprises a bent slotted oblong hole 17 which is parallel to the xz plane. Two guide bolts of a fetcher lever 19 are guided in the slotted oblong hole 17 of the slotted guide 16, to which a thread finger carrier 20 is fixed. The fetcher lever 19 is hingedly connected to a piston rod 22 of a double-acting pneumatic cylinder 23 via a connecting lever 21. A transmission movement of the connecting lever 21 is guided in a base body 24 via an oblong hole 25 extending parallel to the y-direction. Together with the lever gear comprising the levers 19, 21, the pneumatic cylinder 23 constitutes a thread finger drive 26 of the thread finger assembly 12.

The thread finger assembly 12 is mounted on the lower housing portion 4 of the sewing machine 1 via the base body 24.

At the beginning of a seam, the sewing machine 1 operates the thread finger assembly 12 as follows:

As soon as the sewing material comes to rest on the stitch plate 11 a in the correct relative position, the formation of the first stitch of the seam to be sewn is triggered. For this purpose, the two sewing needles 6, 7, which each guide an upper thread 13, penetrate the sewing material and the stitch plate 11 a from above through their respective assigned stitch holes. After reaching a bottom dead center, the sewing needles 6, 7 are moved upwards again a little, so that two upper thread loops are formed under the sewing material between the stitch plate 11 a and the hooks 9, 10.

Subsequently, the thread fingers 14, 15 are transferred from a neutral position, which may correspond to the loop pull-out position, to the loop engagement position (cf. e.g. FIG. 3). Here, the fingertips of the thread fingers 14, 15 penetrate into the formed upper thread loops.

To drive this displacement actuation into the loop engagement position, the piston rod 22 of the pneumatic cylinder 23 is extended.

Subsequently, the thread fingers are brought back into the loop pull-out position by retraction of the piston rod 22, wherein the catcher hooks 15 a take along the respective upper thread 13 and pull an upper thread beginning piece in each case downwards through the sewing material, out of the sewing material visible region.

During the subsequent further sewing of the seam, the thread fingers remain in the loop pull-out position or the neutral position. Depending on the topography of the components to be sewn and the course of the seam, the sewing head of the sewing machine 1 is displaced three-dimensionally in space by the arm of the robot so that even difficult-to-access seam locations may be reached. 

1. A sewing machine (1) with a thread finger assembly (12) with at least one thread finger (14, 15), which can be actuated between a loop engagement position for the engagement of the thread finger (14, 15) in a thread loop generated by the sewing machine (1) in a stitch forming region and a loop pull-out position, which is displaced away from the stitch forming region relative to the loop engagement position for pulling out the thread loop with the thread finger (14, 15), with a thread finger drive (26) for actuating the thread finger (14, 15) between the loop engagement position and the loop pull-out position, wherein in the loop engagement position a fingertip of the at least one thread finger (14, 15) is located between a hook (9, 10) and a stitch plate (11 a) of the sewing machine (1).
 2. The sewing machine according to claim 1, wherein the at least one thread finger (14, 15) has a bent configuration.
 3. The sewing machine according to claim 1, wherein the at least one thread finger (14, 15) has a thread catcher hook (15 a) at its free end.
 4. The sewing machine according claim 1, comprising two thread fingers (14, 15) which can be assigned to two thread loops of a two-needle sewing machine (1).
 5. The sewing machine according to claim 1, comprising a slotted guide (16) for guiding a displacement movement of the thread finger (14, 15) between the loop engagement position and the loop pull-out position.
 6. The sewing machine according to claim 1, wherein the thread finger drive (26) is designed as a pneumatic drive.
 7. The sewing machine according to claim 1, wherein the thread finger (14, 15) has a thickness in the direction of the distance between the hook (9, 10) and the stitch plate (11 a) of the sewing machine (1) which is at most 2 mm.
 8. The sewing machine according to claim 1, wherein a width of the thread finger (14, 15) transverse to its longitudinal extension is smaller than 5 mm. 